This invention relates to macromolecular monomers ("macromers" for brevity) of polylactones having a styryl, allyl, or acryloyl "head" (individually and collectively referred to herein as "vinyl functional") group at one end, and a terminal hydroxyl (OH) group at the other end. The polylactone macromer may also be used to initiate block copolymerization with a ring-openable ether or with another lactone monomer to form a new macromer of block copolymer of lactone-ether or lactone-lactone, respectively. The polylactone macromer is copolymerizable through its head group with an olefinically unsaturated copolymerizable monomer. The copolymerization of the macromer with one or more conventional olefinic monomers generates a "polymacromer" with a saturated hydrocarbon backbone having polylactone branches thus resulting in a graft or comb copolymer. Such copolymerization of the macromer of this invention, to form comb copolymers, differs from graft copolymerization in the sequence of formation of the backbone relative to the formation of the graft unit.
Normally, lactones are not copolymerizable with commonly available olefinically unsaturated monomers. The macromers of this invention now makes this possible.
The macromer is formed in commercially acceptable yield by the cationic ring-opening polymerization of a lactone in conjunction with (a) an alkenyl alcohol which functions as the generator of the propagating species, and (b) an oxonium salt, or etherate of boron trifluoride, cationic ring-opening catalyst. The alkenyl alcohol (referred to as the "propagator", because it functions as the `propagating species (OH group) generator` in the presence of a cationic initiator), if substituted, may have substituents which do not interfere with the initiation, propagation and transfer reactions which generate the macromer in a polymerization which has the characteristics of a living polymerization.
U.S. Pat. No. 3,655,631 to Fraser, teaches that lactones are polymerized in the presence of strong organic acids such as halogen activated carboxylic acids or sulfonic acids as catalyst, and a compound having the formula L--CH.sub.2 OH as initiator, wherein L contains ethylenic unsaturation activated by amide or ester linkages, the ethylenic unsaturation being either CH.sub.2 .dbd.CH&lt; or CH.sub.2 .dbd.CH--, but only an acrylic group was exemplified. The resulting terminally unsaturated polylactones were copolymerized with an ethylenically unsaturated monomer, for example, vinyl acetate; and, were used as plasticizer for poly(vinyl chloride) (PVC). But the teaching as to any ethylenically unsaturated group is not as broadly applicable as at first appears. For example, when the ethylenically unsaturated group is a vinyl ether group, the alkenyl alcohol, such as 2-hydroxyether vinyl ether (CH.sub.2 .dbd.CH--O--CH.sub.2 --CH.sub.2 OH) or 4-hydroxybutyl vinyl ether, is an ineffective propagator. The vinyl ether group of the alkenyl alcohol does not survive under the conditions of cationic ring-opening polymerization of lactones and undergo carbocationic polymerization. As a result, the lactone polymers do not have an ethylenically unsaturated head group.
Further, since Fraser was unaware that the OH group could function as the propagating species, he attributed his polymerization to the ester or amide linkage of the alcohol. Thus, the possibility of using the polylactone polymer he made, to initiate a block polymerization with another lactone could not have occurred to him. Still further, it is only because it is now known that the same lactone ring-opening catalysts are effective in the ring-opening polymerization of alkylene oxides, was it possible to arrive at the concept of using an --OH terminated polylactone with an ethylenically unsaturated head group, as the propagator for the formation of a block copolymer.
It should be recognized that, in copending patent applications Ser. Nos. 771,093 and 796,634, I have obtained allyl terminated, and styryl terminated macromers of polyethers by the cationic ring-opening polymerization of ethers using allyl alcohol and styryl alcohol, respectively, as the propagators, in a reaction involving the cationic ring-opening of an ether. However, there was little reason to assume the reaction would be effective in the polymerization of lactones which are esters, or to predict what properties copolymerization of vinyl-functional polylactone macromers might contribute to copolymers formed with them. Nor was there any reason to believe that the carboxylic acid or sulphonic acid catalysts taught by Fraser could be replaced with an oxonium salt or the etherate of boron trifluoride.
It is known that oxonium salts are effective in ring-opening polymerization of oxirane compounds (see U.S. Pat. No. Re. 31,577 to Riew); and that a hydroxyalkylacrylate provides a vinyl functional head group in such a polymerization (see U.S. Pat. No. Re. 31,468). It so happens that triethyloxonium hexachloroantimonate and triethyloxonium tetrafluoroborate are known to be effective in the polymerization of lactones (see "Catalytic Polymerization of epsilon-caprolactone" by Burba, C et al Ger. Offen. DE No. 2123968) but not for providing an unsaturated head group. Since it is critically important that my macromer possess the vinyl head group, the possibility of using an oxonium salt or the etherate of boron trifluoride in conjunction with the vinyl functional propagator was given little weight. Also, it is well known that, because the mechanisms are generally different, an effective catalyst for cationic ring-opening an oxirane to form a polyether, is not likely to be effective for ring-opening a lactone to form a polyester, and vice versa. It was simply the availability of the particular catalysts which instigated the investigation of their activity in conjunction with a vinyl functional propagator which initiated the ring-opening polymerization of lactones, and such activity fortuitously was found to be high.
It is to be noted that the macromers of this invention are formed by cationic ring-opening and not carbocationic polymerization, though both are classified as cationic polymerizations and may even use the same cationic initiator. The cationic ring-opening involves the opening of strained rings of cyclic monomers and the propagating species is an oxonium, sulfonium or ammonium ion; carbocationic polymerization involves substituted olefinic monomers where the propagating species is a carbenium ion.
With the emphasis on the essentiality of the OH propagating sites and the routine use of saturated end groups, the possibility that a vinyl group, and more specifically, an acryloyl, allyl, or styryl end group might survive the conditions of cationic ring-opening polymerization simply escaped noticed. In view of the large number of olefinically unsaturated monomers which undergo polymerization (see the list in Carbocationic Polymerization by Kennedy, J. P. and Marechal, E., Table 3.6, pp 37 et seq., John Wiley & Sons 1982) the fate of the double bond of the propagator under such conditions seemed speculative.